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		<title>three.js webgpu - volumetric caustics</title>
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				<a href="https://threejs.org/" target="_blank" rel="noopener">three.js</a><span>Volumetric Caustics</span>
			</div>

			<small>Real-time volumetric caustics effects.</small>
		</div>

		<script type="importmap">
			{
				"imports": {
					"three": "../build/three.webgpu.js",
					"three/webgpu": "../build/three.webgpu.js",
					"three/tsl": "../build/three.tsl.js",
					"three/addons/": "./jsm/"
				}
			}
		</script>

		<script type="module">

			import * as THREE from 'three/webgpu';

			import { uniform, refract, div, frameId, lightViewPosition, float, positionView, positionViewDirection, screenUV, pass, texture3D, time, screenCoordinate, normalView, texture, Fn, vec2, vec3 } from 'three/tsl';

			import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
			import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';
			import { DRACOLoader } from 'three/addons/loaders/DRACOLoader.js';
			import { ImprovedNoise } from 'three/addons/math/ImprovedNoise.js';

			import { Inspector } from 'three/addons/inspector/Inspector.js';

			import { bayer16 } from 'three/addons/tsl/math/Bayer.js';
			import { bloom } from 'three/addons/tsl/display/BloomNode.js';

			let camera, scene, renderer, controls;
			let postProcessing;
			let gltf;

			init();

			async function init() {

				const LAYER_VOLUMETRIC_LIGHTING = 10;

				camera = new THREE.PerspectiveCamera( 25, window.innerWidth / window.innerHeight, 0.025, 5 );
				camera.position.set( - 0.7, 0.2, 0.2 );

				scene = new THREE.Scene();

				// Light

				const spotLight = new THREE.SpotLight( 0xffffff, 1 );
				spotLight.position.set( .2, .3, .2 );
				spotLight.castShadow = true;
				spotLight.angle = Math.PI / 6;
				spotLight.penumbra = 1;
				spotLight.decay = 2;
				spotLight.distance = 0;
				spotLight.shadow.mapType = THREE.HalfFloatType; // For HDR Caustics
				spotLight.shadow.mapSize.width = 1024;
				spotLight.shadow.mapSize.height = 1024;
				spotLight.shadow.camera.near = .1;
				spotLight.shadow.camera.far = 1;
				spotLight.shadow.bias = - .003;
				spotLight.shadow.intensity = .95;
				spotLight.layers.enable( LAYER_VOLUMETRIC_LIGHTING );
				scene.add( spotLight );

				// Model / Textures

				const dracoLoader = new DRACOLoader();
				dracoLoader.setDecoderPath( 'jsm/libs/draco/' );
				dracoLoader.setDecoderConfig( { type: 'js' } );

				gltf = ( await new GLTFLoader().setDRACOLoader( dracoLoader ).loadAsync( './models/gltf/duck.glb' ) ).scene;
				gltf.scale.setScalar( .5 );
				scene.add( gltf );

				const causticMap = new THREE.TextureLoader().load( './textures/opengameart/Caustic_Free.jpg' );
				causticMap.wrapS = causticMap.wrapT = THREE.RepeatWrapping;
				causticMap.colorSpace = THREE.SRGBColorSpace;

				// Material

				const duck = gltf.children[ 0 ];
				duck.material = new THREE.MeshPhysicalNodeMaterial();
				duck.material.side = THREE.DoubleSide;
				duck.material.transparent = true;
				duck.material.color = new THREE.Color( 0xFFD700 );
				duck.material.transmission = 1;
				duck.material.thickness = .25;
				duck.material.ior = 1.5;
				duck.material.metalness = 0;
				duck.material.roughness = .1;
				duck.castShadow = true;

				// TSL Shader

				const causticOcclusion = uniform( 1 );

				const causticEffect = Fn( () => {

					const refractionVector = refract( positionViewDirection.negate(), normalView, div( 1.0, duck.material.ior ) ).normalize();
					const viewZ = normalView.z.pow( causticOcclusion );

					const textureUV = refractionVector.xy.mul( .6 );

					const causticColor = uniform( duck.material.color );
					const chromaticAberrationOffset = normalView.z.pow( - .9 ).mul( .004 );

					const causticProjection = vec3(
						texture( causticMap, textureUV.add( vec2( chromaticAberrationOffset.negate(), 0 ) ) ).r,
						texture( causticMap, textureUV.add( vec2( 0, chromaticAberrationOffset.negate() ) ) ).g,
						texture( causticMap, textureUV.add( vec2( chromaticAberrationOffset, chromaticAberrationOffset ) ) ).b
					);

					return causticProjection.mul( viewZ.mul( 60 ) ).add( viewZ ).mul( causticColor );

				} )().toVar();

				duck.material.castShadowNode = causticEffect;

				duck.material.emissiveNode = Fn( () => {

					// Custom emissive for illuminating backside of the mesh based on the caustic effect and light direction

					const thicknessPowerNode = float( 3.0 );

					const scatteringHalf = lightViewPosition( spotLight ).sub( positionView ).normalize();
					const scatteringDot = float( positionViewDirection.dot( scatteringHalf.negate() ).saturate().pow( thicknessPowerNode ) );

					return causticEffect.mul( scatteringDot.add( .1 ) ).mul( .02 );

				} )();

				// Ground

				const textureLoader = new THREE.TextureLoader();
				const map = textureLoader.load( 'textures/hardwood2_diffuse.jpg' );
				map.wrapS = map.wrapT = THREE.RepeatWrapping;
				map.repeat.set( 10, 10 );

				const geometry = new THREE.PlaneGeometry( 2, 2 );
				const material = new THREE.MeshStandardMaterial( { color: 0 } );

				const ground = new THREE.Mesh( geometry, material );
				ground.rotation.x = - Math.PI / 2;
				ground.receiveShadow = true;
				scene.add( ground );

				// Renderer

				renderer = new THREE.WebGPURenderer( { antialias: true } );
				renderer.shadowMap.enabled = true;
				renderer.inspector = new Inspector();
				renderer.setPixelRatio( window.devicePixelRatio );
				renderer.setSize( window.innerWidth, window.innerHeight );
				renderer.setAnimationLoop( animate );
				document.body.appendChild( renderer.domElement );

				// GUI

				const gui = renderer.inspector.createParameters( 'Volumetric Caustics' );
				gui.add( causticOcclusion, 'value', 0, 20 ).name( 'caustic occlusion' );
				gui.addColor( duck.material, 'color' ).name( 'material color' );

				// Post-Processing

				postProcessing = new THREE.PostProcessing( renderer );

				// Layers

				const volumetricLightingIntensity = uniform( .7 );

				const volumetricLayer = new THREE.Layers();
				volumetricLayer.disableAll();
				volumetricLayer.enable( LAYER_VOLUMETRIC_LIGHTING );

				// Volumetric Fog Area

				function createTexture3D() {

					let i = 0;

					const size = 128;
					const data = new Uint8Array( size * size * size );

					const scale = 10;
					const perlin = new ImprovedNoise();

					const repeatFactor = 5.0;

					for ( let z = 0; z < size; z ++ ) {

						for ( let y = 0; y < size; y ++ ) {

							for ( let x = 0; x < size; x ++ ) {

								const nx = ( x / size ) * repeatFactor;
								const ny = ( y / size ) * repeatFactor;
								const nz = ( z / size ) * repeatFactor;

								const noiseValue = perlin.noise( nx * scale, ny * scale, nz * scale );

								data[ i ] = ( 128 + 128 * noiseValue );

								i ++;

							}

						}

					}

					const texture = new THREE.Data3DTexture( data, size, size, size );
					texture.format = THREE.RedFormat;
					texture.minFilter = THREE.LinearFilter;
					texture.magFilter = THREE.LinearFilter;
					texture.wrapS = THREE.RepeatWrapping;
					texture.wrapT = THREE.RepeatWrapping;
					texture.unpackAlignment = 1;
					texture.needsUpdate = true;

					return texture;

				}

				const noiseTexture3D = createTexture3D();

				const smokeAmount = uniform( 3 );

				const volumetricMaterial = new THREE.VolumeNodeMaterial();
				volumetricMaterial.steps = 20;
				volumetricMaterial.offsetNode = bayer16( screenCoordinate.add( frameId ) ); // Add dithering to reduce banding
				volumetricMaterial.scatteringNode = Fn( ( { positionRay } ) => {

					// Return the amount of fog based on the noise texture

					const timeScaled = vec3( time.mul( .01 ), 0, time.mul( .03 ) );

					const sampleGrain = ( scale, timeScale = 1 ) => texture3D( noiseTexture3D, positionRay.add( timeScaled.mul( timeScale ) ).mul( scale ).mod( 1 ), 0 ).r.add( .5 );

					let density = sampleGrain( 1 );
					density = density.mul( sampleGrain( .5, 1 ) );
					density = density.mul( sampleGrain( .2, 2 ) );

					return smokeAmount.mix( 1, density );

				} );

				const volumetricMesh = new THREE.Mesh( new THREE.BoxGeometry( 1.5, .5, 1.5 ), volumetricMaterial );
				volumetricMesh.receiveShadow = true;
				volumetricMesh.position.y = .25;
				volumetricMesh.layers.disableAll();
				volumetricMesh.layers.enable( LAYER_VOLUMETRIC_LIGHTING );
				scene.add( volumetricMesh );

				// Scene Pass

				const scenePass = pass( scene, camera ).toInspector();
				scenePass.name = 'Scene';

				const sceneDepth = scenePass.getTextureNode( 'depth' );
				sceneDepth.name = 'Scene Depth';

				// Material - Apply occlusion depth of volumetric lighting based on the scene depth

				volumetricMaterial.depthNode = sceneDepth.sample( screenUV );

				// Volumetric Lighting Pass

				const volumetricPass = pass( scene, camera, { depthBuffer: false, samples: 0 } ).toInspector( 'Volumetric Lighting / Raw' );
				volumetricPass.name = 'Volumetric Lighting';
				volumetricPass.setLayers( volumetricLayer );
				volumetricPass.setResolutionScale( .5 );

				// Compose and Denoise

				const bloomPass = bloom( volumetricPass, 1, 1, 0 ).toInspector( 'Volumetric Lighting / Mip-Chain Gaussian Blur' );
				bloomPass.name = 'Bloom';

				const scenePassColor = scenePass.add( bloomPass.mul( volumetricLightingIntensity ) );

				postProcessing.outputNode = scenePassColor;

				// Controls

				controls = new OrbitControls( camera, renderer.domElement );
				controls.target.z = - .05;
				controls.target.y = .02;
				controls.maxDistance = 1;

				window.addEventListener( 'resize', onWindowResize );

			}

			function onWindowResize() {

				camera.aspect = window.innerWidth / window.innerHeight;
				camera.updateProjectionMatrix();

				renderer.setSize( window.innerWidth, window.innerHeight );

			}

			function animate() {

				for ( const mesh of gltf.children ) {

					mesh.rotation.y -= .01;

				}

				controls.update();

				postProcessing.render();

			}

		</script>
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